The present invention relates to devices for unfolding and refolding a control surface, that is, a fin or fin members from the body of an airborn projectile, such as a missile and the like. Conventional fin development mechanisms use either simple mechanical spring mechanisms, or pyrotechnic and pneumatic techniques that are irreversible, that is, once the fin is deployed to an unfolded position it cannot be refolded. Should the launch of such a missile be canceled the missile then cannot be returned to its stored position. Further, the presence of pyrotechnics presents a hazard to operational personnel, the missile itself and the missile-carrying aircraft. In the case of pneumatic operation a charged gas pressure storage vessel is required for unlocking torsional springs which then snap the fin into place. A pressure source might well prove hazardous in an airborn environment, not to mention the added weight of the storage vessel. There is, therefore, a genuine need for a retractable fin deployment mechanism which will avoid the above deficiencies.